Magnolia / Aurelia / Cecelia / Octavia / Cordelia / Ophelia / Antonia - these names are similarly regal, feminine, and strong, but Magnolia has a nice Southern (USAian) flare that gives it more character. Aurelia can be a bit of a tongue twister, and it's a hard name for kidlets to say (not that that's overly important). Cecelia has a really unfortunate meaning, but it's got a nice sound to it. Have you also considered Cecily? Less common, has a nice feminine sweetness to it. Octavia is more lovely than all of the others combined. So unusual! But beautiful. Cordelia and Ophelia have the Shakespearean resonance, so that's something. I wish I could love Ophelia, but it reminds me of all those awful words that end in "philia." Also consider Ofelia, either pronounced the English way or oh-FAY-li-ya or oh-FELL-i-ya

Leila or Layla / Lailia / Lilia / Isla - not a huge fan, kind of insubstantial sounding...too soft with all those L's.

Cosmonaut, I think we'll want to give our daughter (someday!) one name that we really love and one name that symbolizes strength or wisdom in some way, or that honors a strong female from history or literature. It's important to me to emphasize female role models, and we're both huge history and literature geeks, so that will probably influence it in some way… but I also love girly names, hence Magnolia and Arabella. So that's why there's a weird mash up of soft, flowy names and strong girl names like Matilda and Josephine.

Of your names I really love Linnea but I was having a hard time pairing it with a middle name from only the mn list. Out of both lists, however, I think I like LinneaPenelope or LinneaMadelineJune or something to that extent.